Recently, display devices are required to have reduced weight and thickness as personal computers and television receivers decrease in weight and thickness. In response to such requirements, flat-panel display devices such as liquid crystal displays (LCDs) are becoming more common in place of cathode-ray tube (CRT) displays.
These days, LCDs are widely used not only as display devices for computers but also as display devices for television receivers. As such, there are growing needs for displaying moving images on LCDs. However, LCDs generally have a response speed that is lower than a response speed of display devices such as CRTs. On this account, in general, LCDs have a disadvantage such that it is difficult to appropriately display moving images.
In order to solve the problem of the response speed of LCDs, there is a known method for driving liquid crystals by applying, to a liquid crystal layer, a driving voltage (overshoot driving voltage) that is higher than a predetermined gray scale voltage of an input image signal of a current frame or a driving voltage (undershoot driving voltage) that is lower than the predetermined gray scale voltage, according to a combination of the input image signal of the current frame and an input image signal of a frame immediately preceding (i.e., one vertical display period before) the current frame. Furthermore, as a method obtained by developing this driving method, there is another known method for driving liquid crystals by applying, to a liquid crystal layer, a driving voltage that is higher or lower than a predetermined gray scale voltage of an input image signal of a current frame, according to a combination of the input image signal of the current frame and an image signal corresponding to a gray scale (an image) that is assumed to be actually displayed on the liquid crystal display in a frame immediately preceding the current frame (i.e., an image signal that causes the assumed gray scale to be displayed on the liquid crystal display, when the image signal is applied until the liquid crystals are aligned in a steady state). Hereinafter in the present specification, these methods for driving liquid crystals are referred to as an overshoot drive (OS drive) or an emphasis conversion process.
It is also known that the response speed of liquid crystal is highly dependent on temperature. For the purpose of eliminating this temperature dependency of the response speed of liquid crystal, there is known a technique, i.e., a liquid crystal display device described below. The liquid crystal display device includes a plurality of tables each storing an emphasis conversion parameter corresponding to a combination of image data of a current frame and an image signal of a frame immediately preceding the current frame (or an image signal corresponding to a gray scale that is assumed to be actually displayed on the liquid crystal display in the frame immediately preceding the current frame). The tables are provided so as to correspond respectively to a plurality of temperature ranges. In accordance with a result of temperature detection by a temperature sensor which is provided in the liquid crystal display device, one table is selected from the plurality of tables. With use of the selected table, an overshoot drive is performed.
As an example, Patent Literature 1 discloses a liquid crystal display device including: a plurality of OS look-up tables corresponding respectively to a plurality of temperature ranges, each of the plurality of OS look-up tables storing in advance an emphasis conversion parameter corresponding to a combination of image data of a current frame and image data of a frame immediately preceding the current frame; a temperature sensor detecting an in-device temperature of the liquid crystal display device; an installation configuration detecting section detecting an installation configuration of the device; a control CPU selecting, by switching, any of the plurality of OS look-up tables based on temperature data detected by the temperature sensor and installation configuration data detected by the installation configuration detecting section; and an emphasis conversion section obtaining, in reference to an OS look-up table selected by switching, emphasis conversion data that corrects optical response characteristics of a liquid crystal display panel.
As another example, Patent Literature 2 discloses a liquid crystal display device that corrects optical response characteristics of a liquid crystal display panel by performing, based on an emphasis conversion parameter obtained as a result of a comparison between image data of a current frame and image data of a frame immediately preceding the current frame, an emphasis conversion on image data which is to be supplied to the liquid crystal display panel. This liquid crystal display device includes: temperature detection means detecting an in-device temperature of the liquid crystal display device; and control means correcting temperature data detected by the temperature detection means so as to compensate a difference between the detected temperature data and the temperature of the liquid crystal display panel, and, based on thus corrected temperature data, variably controlling the emphasis conversion parameter. More specifically, the control means includes an operation expression storage section storing operation expressions for, e.g., adding to/subtracting from the temperature data detected by the temperature sensor, a predetermined value which is determined in advance in accordance with, for example, a mounting position of the temperature sensor (a relative positional relation of the temperature sensor with respect to the liquid crystal display panel); and a computing section performing, with use of an operation expression read out from the operation expression storage section, a correction operation on the temperature data detected by the temperature sensor. The technique disclosed in Patent Literature 2 thus compensates a difference between the temperature detected by the temperature sensor and an actual temperature of the liquid crystal display panel. The difference arises from restriction of the mounting position of the temperature sensor.